The building envelope has many purposes, some of which are functional, while others are aesthetic in nature. Two of the most significant functional purposes are controlling water intrusion and controlling air movement.
Most exterior building envelopes are composed of both vertical surfaces (that are walls) and steep or low slope surfaces (that are roofs). With specific regard to the exterior wall, the outer surface is generally covered with a material that is referred to as a siding or cladding.
Behind many types of siding material, is a layer of secondary protection to minimize the passage of water and air. Buildings that are considered light frame construction; i.e., those with either wood or metal studs, usually include a sheathing material. The sheathing is attached to the frame structure. Because many sheathing products are either wood-base or gypsum-base, they will deteriorate if exposed to water for an extended period of time. Accordingly, these types of sheathing products are typically covered with a sheet material to provide secondary protection for the sheathing and structural members.
Therefore, the outer surface of the aforementioned siding or cladding provides both an aesthetic and functional role in that it provides the overall visual appearance of the building and functions to exclude most water from penetrating to the underlying sheathing and frame work construction. The aforementioned layer of secondary protection is intended to stop incidental water from reaching the underlying construction and retard the ingress and egress of air as well.
Many field investigations and laboratory studies have shown that water that enters past the exterior face of the siding may cause damage to the underlying construction if the secondary protection is not present or operational. In addition to the water sensitive sheathing products previously referenced, many other related construction materials will deteriorate due to the long term effects of water intrusion. Also, in conditions of high relative humidity, air that moves through the exterior wall construction may contribute to the water intrusion problem when water vapor condenses on sheathing or structural members. Finally, if water remains on the surface of certain types of wood or paper-based products within the wall system, the growth of certain fungi (mold) may occur.
Some types of mold spores are considered undesirable and may trigger allergic-type reactions in certain individuals with a sensitivity to these fungi. Therefore, it is desirable to control water intrusion and air movement through exterior wall construction, and mitigate the accumulation of water within the exterior wall sheathing and structure. In certain cases, such water will cause: 1) deterioration of the underlying construction materials or components; and 2) foster the growth of fungi/mold which may be an irritant to hyper-sensitive building occupants. The mold concern has been receiving increased attention nationwide to such a point that the insurance industry has found it necessary to increase insurance rates or cease writing certain policies to help offset their losses due to mold damage claims arising therefrom.
To date, individual exterior wall materials and components have been developed and sold without attempting to provide an overall integrated system for controlling water intrusion and air movement in completed wall assemblies.
The instant patent application builds upon two previously cited patents which were recently issued to this inventor. It also draws upon the building diagnostic expertise of the inventor, and provides a new approach for protecting exterior wall sheathing products as well as other underlying building materials. It has been found that elastomeric membrane-like materials such as urethane based coatings or hybrid urethane-silicone coatings can be applied over the surface of certain sheathing products, wood or gypsum based, preferably as a final step in the manufacturing process of theses products. Where sheathing products are not pre-finished with the membrane-like material, these uncoated sheathing products may be readily coated with elastomeric membrane-like materials in the field. Further, the subject application can be used over the entire surface of water sensitive sheathing products (i.e. gypsum and wood based products) as well as the joints between sheets of sheathing boards and around through-wall penetrations. Some types of sheathings, such as rigid foam boards, (Owens Corning® Extruded Polystyrene or equal), foil faced composition products, (Tyco Thermo Ply® or equal) or cement based sheathings, (National Gypsum Company Perma Base® or equal) have water resistant surfaces, and may only require specialized treatment at the joints between sheets and through-wall penetrations in order to control water intrusion and air movement through the exterior wall construction. A combination of several different types of sheathing products sometimes occurs on residenial and light commercial projects.